This invention relates to a method and means for improving the insulation of a piezoelectric stack and to improvements therein.
In the usual utilization of piezoelectric material, (pz), in devices, piezoelectric discs are stacked. Their opposite flat faces are coated with a conductive material in order to enable voltage to be applied over all of the discs in parallel, while the disc displacement is aggregated as a result of the stacking, to obtain optimum axial displacement for the applied voltage. The piezoelectric stack is usually immersed in an insulating medium in order to prevent arc over between the edges of the discs of the stack.
However, failures are frequently encountered in such assemblies because the dielectric strength of the medium insulating the edges of the conducting layers is limited by the electric field strength rather than by the voltage which is applied. A wide variety of insulating materials with widely different dielectric strengths has been tried without any significant alteration in the breakdown rate. As a result of testing and studies to identify the mechanism whereby breakdown is occurring, it is revealed that there is a separation from the dielectric insulation occurring at the interface between the ceramic disc and the insulating medium.